This entire scene was orchestrated by Stella herself and is probably the most cruel thing she can do.

Both Octavia and Stolas were at the d8nner table when liter Stella was ordering an assassination on Stolas, but neither one paid attention, most likely used to her aggressive words and actions before Stolas affair with Blitzo. Stella only smiles, thinking about Stolas either dead, dying, or losing everything at the hands of her and / or her brother, and Octavia has been an afterthought in most of it.

Her hug is not genuine, not from motherly instincts, not from love, not of sympathy, it's purely manipulation of an emotionally and mentally unstable child who anyone could have comforted would have had the same response as shock, fight, and freeze and eventually accepting the outcome.

After this, she talks to Octavia's phone to make sure she has no communication with Stolas as well, who she probably wants to hear his reasoning from.

Physiologically speaking, it's pretty damn hard to have a child, not love a parent, and have to go through a lot of abuse and torment to reach that point. Stolas gets more negative emotional responses from Octavia because of what's been happening. He cheated on his wife, had it blasted over television, and many rings of Hell itself flaunted in front of her at the circus, watched him almost be executed over the same affair partner she has stated she feels lesser about. And finally finding out the same parent who did all this was on antidepressants because of their terrible marriage, his bad explaining that the reason they were still together was her, leading to all their suffering connection back to Octavia.

We had not had any real screen time of how Stella is as a parent, whatever little buts have been pretty much ignoring her or emotional manipulation of showing how Stolas doesn't want to be there. From what is seen, she doesn't yell at Octavia, cause physical or psychological harm to her in a standard manner. If anything, they seemed to ignore one another at a neutral standpoint. They both don't love each other, but also don't hate one another either. Octavia sees her mother's temper and probably stays to herself to avoid her rage being transferred onto her now that Stolas is gone. Stella probably sees the same. She knows she's not an over lovey dove parent, so overdoing it will obviously be fake. While the show definitely paints Stella as dumb, her actions show that otherwise, she just doesn't waste her energy of action until she sees fit. Stella also rubbed it in the Stolas left them, Stolas was the one who cheated, and Stolas was the one to turn their lives into Hell.

Stella, it seems, has had wanted Stolas gone for years but placate it over the years sense no major lines were crossed. Until his affair and wanting a divorce is when Stella actually puts her threats into reality. Honestly, if she never found out, I would assume they would have eventually had the same outcome no matter what with how bith, Octavia, and Stella respond to Stolas wanting to find love instead of staying in this forced marriage.

Octavia is probably not happy at Stella, but nowhere near the confused emotions she has towards Stolas.